Inhaled nitric oxide (NO) diminishes inflammatory responses in vitro and in some animal models of lung inflammation. This study will provide a means to study mechanims involved in NO modulation of local pulmonary inflammation in humans. Several lines of evidence suggest that NO can modulate the inflammatory response in experimental lung inflammation. Nitric oxide donors inhibit inflammatory cytokine produc-tion by human alveolar macrophages in vitro, prevents interleukin-1 (IL-1)-induced neutrophil accumulation and edema in isolated rat lungs, and blocked increases in pulmonary lavage neutrophils, protein, and lung myeloperoxidase content in septic swine. Only limited data are available in humans treated with inhaled nitric oxide for acute lung injury. After 4 days of inhaled NO, patients had a reduction of BAL neutrophil spontaneous H2O2 production, CD11b/CD18 expression, and less IL-6 and IL-8 in BAL fluid compared with patients who did not receive inhaled NO. Nitric oxide remains under investigation for adjunctive therapy for acute lung injury. We are planning to evaluate the ability of NO to alter the inflammatory response associated with segmental endotoxin instillation. Twenty-four volunteers will be studied in a randomized fashion. An initial pilot study will be performed in eight subjects challenged with bronchial endotoxin instillation. Following the endotoxin instillation, four subjects will breathe NO (40 ppm), delivered by an anesthesia non-rebreathing face mask with a reservoir bag, and four subjects will breathe room air through a similar mask. The subjects will breathe through the circuit for 6 hours. The lavage cells will be studied using cell culture, functional studies, surface markers and intracellular cytokines with flow cytometry, and mRNA expression. The lavage supernatant will be evaluated for various inflammatory mediators and markers of inflammatory cell activation. Sequential blood samples will be obtained for total leukocyte counts, as well as plasma levels of inflammatory mediators.